Aircraft in area through 31st

Area residents will likely witness both a low-flying airplane and a helicopter throughout the month of January.

U.S. Geological Survey (USGS) scientists plan to conduct the first comprehensive, high-resolution airborne survey to study the rock layers under a region of northeastern Iowa and southeastern Minnesota.

When the data analysis is complete, resulting state-of-the-art, 3-D subsurface maps will help USGS researchers improve an assessment of mineral and water resources of the region.

Residents and visitors should not be alarmed to witness low-flying aircraft near the Decorah, Iowa, and Spring Grove region. Reports of the aircraft flying over Harmony and Preston have been shared already at the end of December.

"Modern society is critically dependent on clean water and a vast array of minerals to maintain and enhance our quality of life," said USGS director Marcia McNutt.

"The USGS uses the latest technology to find new sources of these valuable commodities, even when buried deep beneath the Earth's surface, and places that information in the public domain to benefit all Americans."

Bob Libra, a geologist for the state of Iowa, shared the following information on Facebook, explaining the survey. "The main driver on this is to learn more about the deep Precambrian age rocks in the area, which may have metallic mineral potential, like those up north.

"The Precambrian rocks are covered with 1,500-plus of sedimentary strata. This should give a great look at the structure of these sedimentary rocks too, folds, faults, etc."

Libra also added that these sedimentary layers are "all screwed up in a circular area below Decorah, which we think resulted from a meteor impact about 400 million years ago. This will help us learn about that too. But the main deal is the deep rocks and metals."

He also pointed out that this survey is not about frac sand. "Economic frac sand is going to be pretty near the surface (like right below or 100 feet max below), and well records and mapping already show where it's at in 3-D," Libra added.

"We've supplied that info to all interested parties: mining companies, the anti-mining people and the Allamakee County P&Z and health departments."

The surveys will be conducted by an airplane and a helicopter. The airplane is under contract to the USGS through Bell Geospace; the helicopter through Geotech.

The aircrafts will be operated by experienced pilots who are specially trained and approved for low-level flying. All flights are coordinated with the Federal Aviation Administration to ensure flights are in accordance with U.S. law.

The survey area is thought to be part of the 1.1-billion-year-old Midcontinent Rift, a major structure that stretches across much of the central United States. Rocks of the Midcontinent Rift include large volumes of mafic rocks. In the Lake Superior region, these rocks contain significant resources of nickel, copper and platinum group elements.

USGS scientists plan to use the new geophysical data to help determine if there is potential for similar resources to exist in the survey area.

A secondary goal is to evaluate the geologic structure as it relates to water resources. This research is meant to study deep rocks, beneath limestone and sandstone layers.

The helicopter will carry large electromagnetic and magnetic instruments from a cable underneath. A DC-3, retrofitted with modern avionics and gas turbine engines, will carry gravity gradient instruments.

Because different rock types differ in their content of water, magnetic minerals and density, the resulting geophysical maps allow visualization of the geologic structure below the surface.

This survey will be flown in a grid pattern, by both aircraft at different times. East-west lines will be flown one-quarter mile apart at elevations from 100 to 500 feet above the ground, and two and one-half miles apart in a north-south direction. All survey flights will occur during daylight hours.

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